1. CHAPTER 4

2. How molecules are symbolized?
Cl Cl Cl2
Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH)2
How many of each atom are in the following?
a) NaOH
b) Ca(OH)2
c) 3CaCl2
Na = 1, O = 1, H = 1
Ca = 1, O = 2, H = 2
Ca = 3, Cl = 6

3. Law of Conservation of Mass
The law of conservation of mass states that matter can neither be created or destroyed during a chemical reaction. (Antoine Lavoisier said this!)
CH4 + 2O2  CO2 + 2H2O
8 g g  x g g
The mass of CO2 needed is 22 g.
**(the mass is the same on the right side and left side)

4. Physical changes in matter 404
A Physical change is a change in the shape and appearance of matter. It is reversible.
Tearing
Cutting
Folding
Phase Changes*
Mixing
Dissolving

5. Chemical changes in matter
A chemical change changes the nature and characteristic properties of matter. It is not reversible.
Burning
Rusting
Cooking

6. There are clues that a chemical change is occurring:
Signs of chemical change:
Bubbles are forming
Precipitate forms
Color change
Heat or light is given off
Electricity produced

7. Types of Chemical Changes (p117)
There are different types of changes and in chapter 4 we will study some of them:
acid- base neutralization (404)
combustion (404)
cellular respiration (404)
photosynthesis (404)
synthesis (466)
decomposition (466)
precipitation (466)
oxidation (466)

8. Neutralization (404)
Neutralization is when an acid and a base combine to produce salt and water.
Example 1:
HCl + NaOH --> NaCl +H2O
(acid) + (base) --> (salt) + (water)
Example 2: Acid rain is causing the acidification of Quebec’s lakes & soil. Lime (Ca(OH)2) is a base and can be added to lakes and soil to neutralize the acid and bring the pH of the lake or soil back to 7.

9. Combustion (404) p. 121 Combustion releases a large amount of energy.
You need 3 things for combustion:
a fuel (wood or propane)
an oxidizing agent (air, oxygen)
a certain temperature

10. There are 3 types of combustion:
Rapid combustion: it releases a great deal of energy in a short period of time (a log fire, a burning candle)
Spontaneous combustion: It is often unpredictable and could be disastrous. (on a very hot and dry summer day, wood can catch fire spontaneously - forest fires)
Slow combustion: Occurs over a long period of time. (fermentation and cellular respiration)

11. Cellular Respiration (404)
It is a slow combustion
It takes place in our cells.
In humans, it keeps our body temperatures at around 37oC.
Glucose(sugar) and oxygen are used to generate energy. It produces carbon dioxide and water.

12. EQUATION FOR RESPIRATION
CARBON DIOXIDE
GLUCOSE
C6H12O6 +
6O2
6CO2 +
6H2O +
ENERGY
OXYGEN
WATER

13. PHOTOSYNTHESIS (404) Plants make their own food
Through photosynthesis, plants use solar energy to make glucose (sugar) and oxygen from carbon dioxide and water.
Without photosynthesis, life would not exist on Earth.

14. EQUATION FOR PHOTOSYNTHESIS
WATER
OXYGEN
6 CO2 +
6 H2O +
ENERGY
C6H12O6 +
6 O2
CARBON DIOXIDE
GLUCOSE

15. General Equation: A + B  AB
Synthesis (466) p.118
C + O CO2 O C +  O C O C O C O C O C O C O C O C O C O C O C O C O C O C O C
General Equation: A + B  AB

16. General Equation: AB  A + B
Decomposition (466)  Cl Na Cl + Na
General Equation: AB  A + B

17. Precipitation (466) p.118
When you combine two solutions and a solid is formed. The solid is called a precipitate.
On page 118 of your textbook, you can find out how you can predict whether combining two liquids will give a precipitate.

18. Oxidation (466) p. 120
Oxidation is a chemical change involving oxygen or a substance with properties similar to those of oxygen. Ex: rust forming

19. Balancing Chemical Equations
Atoms are neither created or destroyed, only rearranged in a chemical reaction.
The number of a particular atom is the same on both sides of a chemical equation
Example:
Mg + O2  MgO O Mg +  Mg O
However, this is not balanced!
Left: Mg = 1, O = 2
Right: Mg = 1, O = 1

20. EXOTHERMIC and ENDOTHERMIC Reactions 466 (p114)
Exothermic Reactions
These chemical changes give off heat energy.
C(s) + O2(g) CO2 (g) kJ
Endothermic Reactions
These reactions take in heat energy from their surroundings.
N2 (g) + O2 (g) kJ NO (g)

21. Endothermic = absorbing energy
Exothermic = releasing energy
Law of conservation of energy = release and absorption of energy must be equal

22. reaction
Exothermic reaction, heat is given off & temperature of the water rises
reaction
Endothermic reaction, heat is taken in & temperature of the water drops

23. Is it ENDO or EXO?
Indicate if the following are exothermic or endothermic?
A) gasoline burning
exothermic
B) a lake of freezing
c) clothes drying on the line
endothermic

24. Exothermic energy level diagram
DH (‘delta H’) is the symbol for the ‘change in energy’.
In an exothermic reaction the products have less energy than the reactants.
DH is negative for an exothermic reaction.

25. Endothermic energy level diagram
In an endothermic reaction the products have more energy than the reactants.
DH is positive for an endothermic reaction.

26. Making and breaking bonds.
(466)

27. DH = H bonds broken - H bonds formed (reactants) (products)
Each type of chemical bond has a characteristic bond energy.
Breaking bonds requires energy. It is endothermic.
Making new bonds gives out energy. It is exothermic.
The energy associated for different bonds can be found on page 115 of your textbook.
To calculate DH use the formula:
DH = H bonds broken - H bonds formed
(reactants) (products)

28. Single bonds energies (kJ/mol)

29. Double and triple bonds energies (kJ/mol)

30. H2(g) + Br2(g) --> 2HBr(g)
Calculate the DH for the above reaction.
You need to use the values of page 115 of your textbook.
DH = H bonds broken - H bonds formed
DH =( ) - ( )
DH = kJ/mol
Bonds Broken:
H-H kJ/mol
Br-Br 192 kJ/mol
Bonds Formed:
H-Br kJ/mol

31. Radioactivity (466) p126
Radioactivity is a natural process where an unstable atom spontaneously transforms into a stable atom and in the process releases energy in the form of radiation.
Henri Becquerel discovered the first radioactive element, Uranium. (1896)
There are 3 types of radioactivity:
Phosphorescent zinc sulfide detection screen + –
Strong magnetic or electrostatic field
Lead block
Radioactive substance   

32. Types of Radiation (466)
Alpha () particles are deflected towards the negative pole because they are positive particles. They can be stopped with a sheet of paper.
Beta () particles are deflected towards the positive pole because they are negative particles. A sheet of foil 4mm thick can stop them.
Gamma (g) rays are neutral. They have the greatest penetrating power. A very dense material (like lead) can stop them.

33. Radiation Protection

34. Uses of Radioactivity(466)
Treating cancer (kills cancer cells)
Internal inspection
Smoke detectors
Sterilisation
Food irradiation (to increase the shelf life of food)

35. Radioactive Decay (466)
Radioactive elements are unstable. They decay, change, into different
elements over time. Here are some facts to remember:
The half-life of an element is the time it takes for half of the
material you started with to decay. Remember, it doesn’t matter how
much you start with. After 1 half-life, half of it will have decayed.
Each element has it’s own half-life ( page 129)
The half-life of each element is constant. It’s like a clock keeping perfect time.
Now let’s see how we can use half-life to determine the
age of a rock or other artifact.

36. The half-life of this element is 1 million years.
Questions may involve
graphs like this one. The most
common questions are:
"What is the half-life of this
element?"
**Just remember that at the end
of one half-life, 50% of the
element will remain. Find 50%
on the vertical axis, Follow the
blue line over to the red curve
and drop straight down to find
the answer:
Answer:
The half-life of this element is 1 million years.

37. After 2 million years 25% of the original material will remain.
Another common question is:
"What percent of the material
originally present will remain
after 2 million years?"
Find 2 million years on the
bottom, horizontal axis. Then
follow the green line up to the
red curve. Go to the left and
find the answer.
Answer:
After 2 million years 25% of the original material
will remain.

38. Nuclear reactions involve protons and neutrons in the nucleus.
Nuclear Reactions p
Nuclear reactions involve protons and neutrons in the nucleus.
During a nuclear reaction, the nucleus can lose or gain protons and neutrons.
Compared to chemical reactions, nuclear reactions involve enormous energy change.

39. DID YOU KNOW?
Albert Einstein was the first scientist to realize the enormous amount of potential energy that is available in matter.
He realized that mass and energy are related by the following equation: E=mc2
The c represents the speed of light (3.00x 108 m/s), E is energy and m is mass. Since c is so big, then even a small mass can be converted into an enormous amount of energy.
This explain how a nuclear weapon, like the atomic bomb is so much more powerful than a chemical reaction like a bomb made with dynamite.

40. Nuclear Fission
Nuclear fission can be induced by bombarding atoms with neutrons. (discover by Otto Hahn, a German chemist)
The nuclei of the atom is split into 2 or more lighter
atomic nuclei. (fission means to split)
Nuclear fission is the nuclear reaction that is most
commonly used by humans.

41. Nuclear Fission with Uranium
235U n Ba Kr + 3 1n +
Energy

42. The Fission Process p. 130
A neutron travels at high speed towards a uranium-235 nucleus. U
235 92 n 1

43. The Fission Process
A neutron travels at high speed towards a uranium-235 nucleus. U
235 92 n 1

44. The Fission Process
A neutron travels at high speed towards a uranium-235 nucleus. U
235 92 n 1

45. The Fission Process
The neutron strikes the nucleus which then captures the neutron. U
235 92 n 1

46. The Fission Process
The nucleus changes from being uranium-235 to uranium-236 as it has captured a neutron. U
236 92

47. The Fission Process The uranium-236 nucleus formed is very unstable.
It transforms into an elongated shape for a short time.

48. The Fission Process The uranium-236 nucleus formed is very unstable.
It transforms into an elongated shape for a short time.

49. The Fission Process The uranium-236 nucleus formed is very unstable.
It transforms into an elongated shape for a short time.

50. The Fission Process
It then splits into 2 fission fragments and releases neutrons. n 1
141 56 Ba n 1 92 36 Kr n 1

51. The Fission Process
It then splits into 2 fission fragments and releases neutrons. n 1
141 56 Ba n 1 92 36 Kr n 1

52. The Fission Process
It then splits into 2 fission fragments and releases neutrons. n 1
141 56 Ba n 1 92 36 Kr n 1

53. The Fission Process
It then splits into 2 fission fragments and releases neutrons. n 1
141 56 Ba n 1 92 36 Kr n 1

54. U + Ba n 3 Kr U + Cs n 2 Rb Nuclear Fission Examples 235 92 141 56 13 Kr 36 U
235 92 + Cs
138 55 n 1 2 Rb 96 37

55. H + He n Energy Nuclear Fusion p.131 2 1 4 3
In nuclear fusion, two nuclei with low mass numbers combine to produce a single nucleus with a higher mass number.
The most common type of fusion reaction is the reaction in the sun, hydrogen nuclei fuse to form helium. H 2 1 + He 4 n 3
Energy

56. Nuclear Fusion Fusion small nuclei combine 2H + 3H 4He + 1n + 1 1 2 0
Occurs in the sun and other stars
Energy

57. The Fusion Process H 2 1 H 3 1

58. The Fusion Process H 2 1 H 3 1

59. The Fusion Process H 2 1 H 3 1

60. The Fusion Process H 2 1 H 3 1

61. The Fusion Process

62. The Fusion Process

63. The Fusion Process

64. The Fusion Process

65. The Fusion Process n 1 He 4 2
ENERGY

66. The Fusion Process n 1 He 4 2
ENERGY

67. The Fusion Process n 1 He 4 2
ENERGY

68. The Fusion Process n 1 He 4 2
ENERGY